Corona ignition device with improved seal

ABSTRACT

An electrically conductive glass seal for providing a hermetic bond between an electrically conductive component and an insulator of a corona igniter is provided. The glass seal is formed by mixing glass frits, binder, expansion agent, and electrically conductive metal particles. The glass frits can include silica (SiO 2 ), boron oxide (B 2 O 3 ), aluminum oxide (Al 2 O 3 ), bismuth oxide (Bi 2 O 3 ), and zinc oxide (ZnO); the binder can include sodium bentonite or magnesium aluminum silicate, polyethylene glycol (PEG), and dextrin; the expansion agent can include lithium carbonate; and the electrically conductive particles can include copper. The finished glass seal includes the glass in a total amount of 50.0 to 85.0 weight (wt. %), and electrically conductive metal particles in an amount of 15.0 to 50.0 wt. %, based on the total weight of the glass seal.

CROSS REFERENCE TO RELATED APPLICATION

This U.S. patent application claims the benefit of U.S. provisionalpatent application Ser. No. 62/035,452, filed Aug. 10, 2014, the entirecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to glass seals for ignition devices,and more particular to corona igniters including glass seals, andmethods of forming the same.

2. Related Art

Glass seals are oftentimes used to form a hermetic bond between anelectrically conductive component, such as central electrode, and aninsulator of an ignition device, for example a corona igniter. The glassseal of the corona igniter is typically formed by disposing a glasspowder in a bore of the insulator, and then subsequently firing theinsulator, central electrode, and glass powder together in a furnace.The heat also causes certain components of the glass seal to expand andthus form the hermetic bond between the insulator and central electrode.However, as the glass powder between the central electrode and insulatormelts and expands, gas bubbles or gas pores are formed, and thosebubbles or pores remain in the glass seal of the finished coronaigniter, even after the glass seal cools to room temperature. Thus, whenthe corona igniter is used in an internal combustion engine andsubjected to a high electric field, the electric field causes the gascontained in the bubbles or pores to become ionized and form corona. Theionized gas generates a cascade of ionized charges which transmits heatto the surrounding solid insulator. A thermal breakdown mechanismoccurs, which can create a dielectric breakdown. The effect of thisdielectric breakdown caused by the gas is especially pronounced when thebubbles or pores are large, in which case dielectric failure of theinsulator can occur. Dielectric punctures through the insulator to theexpanded glass seal could potentially result in failure of the coronaigniter.

SUMMARY OF THE INVENTION

One aspect of the invention provides an electrically conductive glassseal having an electrical conductivity ranging from 9×10⁶ S/m to 65×10⁶S/m for providing a hermetic bond between an electrically conductivecomponent and an insulator of a corona igniter. The glass seal includesat least one glass in a total amount of 50.0 to 85.0 weight percent (wt.%), and electrically conductive metal particles in an amount of 15.0 to50.0 wt. %, based on the total weight of the glass seal. The glass sealalso includes gas-filled pores in an amount of 25.0 to 75.0 volumepercent (vol. %), based on the total volume of the glass seal.

Another aspect of the invention provides a corona igniter including aninsulator surrounding an electrically conductive component, and anelectrically conductive glass seal providing a hermetic bond between theelectrically conductive component and the insulator. The electricallyconductive glass seal includes at least one glass in a total amount of50.0 to 85.0 wt. %, and electrically conductive metal particles in anamount of 15.0 to 50.0 wt. %, based on the total weight of the glassseal. The glass seal has an electrical conductivity ranging from 9×10⁶S/m to 65×10⁶ S/m. The glass seal also includes gas-filled pores in anamount of 25.0 to 75.0 vol. %, based on the total volume of the glassseal.

Yet another aspect of the invention provides a method of manufacturing aglass seal for a corona igniter. The method includes providing a mixtureincluding at least one glass frit in a total amount of 48.8 to 85.0 wt.%, a binder in an amount of 0.1 to 3.0 wt. %, an expansion agent in anamount of 0.1 to 1.0 wt. %, and electrically conductive metal particlesin an amount of 14.8 to 50.0 wt. %, based on the total weight of themixture. The method further includes firing the mixture to form theglass seal, wherein the glass seal has an electrical conductivityranging from 9×10⁶ S/m to 65×10⁶ S/m.

Another aspect of the invention provides a method of manufacturing acorona igniter including an electrically conductive glass seal providinga hermetic bond between an electrically conductive component and aninsulator. The method includes disposing a mixture between theelectrically conductive component and the insulator, wherein the mixturecomprises at least one glass frit in a total amount of 48.8 to 85.0 wt.%, a binder in an amount of 0.1 to 3.0 wt. %, an expansion agent in anamount of 0.1 to 1.0 wt. %, and electrically conductive metal particlesin an amount of 14.8 to 50.0 wt. %, based on the total weight of themixture. The method further includes firing the mixture to form theglass seal, wherein the glass seal has an electrical conductivityranging from 9×10⁶ S/m to 65×10⁶ S/m.

The electrically conductive particles surround any gas filled poreswhich are formed during firing of the glass seal. The electricallyconductive particles eliminate the electric field across the pores whenthe corona igniter is used in an internal combustion engine andsubjected to a high electric field. Thus, ionization of the gas whichcould initiate dielectric breakdown and dielectric puncture through theinsulator of the corona igniter is eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a cross-sectional view of a corona igniter including anelectrically conductive glass seal according to an exemplary embodimentof the invention;

FIG. 2 is an illustration of the electrically conductive glass seal ofFIG. 1 along line A-A after a firing step, which includes glass,conductive metal particles, and gas-filled pores; and

FIG. 2A is an enlarged view of a portion of FIG. 2.

DESCRIPTION OF THE ENABLING EMBODIMENT

One aspect of the invention provides a corona igniter 20 including anelectrically conductive glass seal 22 providing a hermetic bond betweenat least one electrically conductive component, such as a centralelectrode 24, and an insulator 26, as shown in FIG. 1. The compositionof the glass seal 22 reduces the potential for dielectric breakdown andthus dielectric punctures through the insulator 26 when the centralelectrode 24 or other electrically conductive components of the coronaigniter 20 receives a high radio frequency electric field during use inan internal combustion engine.

The electrically conductive glass seal 22 is formed from a powdermixture which includes a mixture of electrically conductive particles,at least one binder, an expansion agent, and glass frits. In anexemplary embodiment, the glass seal 22 includes the electricallyconductive particles in an amount of 15.0 to 50.0 weight percent (wt.%), and preferably 20.0 wt. %, based on the total weight of the glassseal 22. The powder used to form the glass seal 22 typically includesthe electrically conductive particles in an amount of 14.8 to 50.0 wt.%, based on the total weight of the powder used to form the glass seal22.

The electrically conductive particles can include a single material or amixture of different materials. Any conductive metal can be used to formthe electrically conductive particles, but in the exemplary embodiment,the electrically conductive particles consist of, or essentially of,copper. Also, the electrically conductive particles can comprise variousforms, but in the exemplary embodiment, they are provided in the form ofcopper flakes having a particle size of less than 325 mesh, or 45microns. The electrically conductive particles cause the glass seal 22to be electrically conductive. In one exemplary embodiment, the glassseal 22 has an electrical conductivity ranging from 9×10⁶ S/m to 65×10⁶S/m, or above 9×10⁶ S/m, and preferably above 30×10⁶ S/m.

As described above, in comparative corona igniters includingnon-conductive glass seals, the gas bubbles or pores become ionized andform corona during service, which can lead to dielectric failure of theinsulator. However, when the electrically conductive glass seal 22 ofthe present invention is used in the corona igniter 20, the electricallyconductive particles surround the gas bubbles or pores and thuseliminate the electric field across the bubbles or pores when the highradio frequency voltage is applied to the corona igniter 20. Since nocorona discharge is formed along the bubbles or pores of theelectrically conductive glass seal 22, the initiation mechanism forionization breakdown and dielectric puncture through the insulator 26 iseliminated.

The powder used to form the electrically conductive glass seal 22 alsoincludes the at least one binder in an amount up to 3.0 wt. %, based onthe total weight of the powder used to form the glass seal 22. Thebinders help adhere the components of the glass seal 22 together whenthe glass seal 22 is introduced into the bore of the insulator 26.Preferably, the glass seal 22 includes a mixture of inorganic binder andsynthetic or natural organic binders. When the powder used to form theglass seal 22 is heated to a glass melting temperature during the firingstep, at least a portion of the binder, typically the organic binder,burns off and thus is not present in the composition of the fired glassseal 22.

In the exemplary embodiment, the powder used to form the glass seal 22includes the inorganic binder in an amount up to 2.0 wt. %, or 0.1 to2.0 wt. %, and preferably 1.0 wt. %, based on the total weight of thepowder used to form the glass seal 22. The inorganic binder can includea single material or a mixture of different materials. Any type ofinorganic binder material can be used in the glass seal 22, buttypically the inorganic binder includes natural or engineered clay. Inthe exemplary embodiment, the inorganic binder consists of, or consistsessentially of, sodium bentonite or magnesium aluminum silicate, whichis sold under the name Veegum®.

The powder used to form the glass seal 22 of the exemplary embodimentalso includes the synthetic or natural organic binder in an amount up to2.0 wt. %, or 0.1 to 2.0 wt. %, and preferably 0.65 wt. %, based on thetotal weight of the powder used to form the glass seal 22. The syntheticor natural organic binder can include a single material or a mixture ofdifferent materials. Any type of synthetic or natural organic bindermaterial can be used in the glass seal 22. However, in the exemplaryembodiment, the synthetic or natural organic binder consists of, orconsists essentially of, polyethylene glycol (PEG) and maltodextrin ordextrin. In this embodiment, the PEG is present in an amount of 0.15 wt.%, and the maltodextrin or dextrin is present in an amount of 0.5 wt. %,based on the total weight of the powder used to form the glass seal 22.

The powder used to form the electrically conductive glass seal 22 alsoincludes the expansion agent in an amount up to 1.0 wt. %, or 0.1 to 1.0wt. %, and preferably 0.5 wt. %, based on the total weight of the powderused to form the glass seal 22. The expansion agent can include a singlematerial or a mixture of different materials. Any type of expansionagent can be used in the glass seal 22, but in the exemplary embodiment,the expansion agent consists of, or consists essentially of lithiumcarbonate. At least a portion of the expansion agent converts from asolid to a gas when heated to the glass melting temperature during thefiring step, thus causing the glass seal 22 to expand.

The balance of the electrically conductive glass seal 22 is typicallyformed of glass. The powder used to from the glass seal 22 includes aplurality of glass frits, which is finely powdered glass. The glassfrits are present in an amount that causes the fired glass seal toinclude glass in an amount of 50.0 to 85.0 wt. %, and preferably 80.0wt. %, based on the total weight of the glass seal 22. In the exemplaryembodiment, the glass fits are present in an amount of 48.8 to 85.0 wt.%, or 50.0 to 84.8 wt. %, and preferably 80.0 wt. %, based on the totalweight of the powder used to form the glass seal 22. In one embodiment,the amount of glass frits used to form the glass seal 22 is selected sothat the ratio between the glass frits and the electrically conductiveparticles is about 4 to 1.

The glass fits comprise ground glass and may contain multiple chemicalelements chemically combined and fused into a single material. Any typeof glass fits known in the art can be used. The glass seal may beformulated with a single glass frit, or multiple glass frits withdifferent chemical compositions and different properties may be blendedtogether. In the exemplary embodiment, multiple glass frits are used.The overall composition of the glass fits includes silica (SiO₂) in anamount of 35 to 40 wt. %, and preferably 38.6 wt. %, based on the totalweight of the glass frits. The glass frits also include boron oxide(B₂O₃) in an amount of 20 to 28 wt. %, and preferably 26.9 wt. %;aluminum oxide (Al₂O₃) in an amount of 10 to 15 wt. %, and preferably11.7 wt. %; bismuth oxide (Bi₂O₃) in an amount of 10.0 to 15.0 wt. %,preferably 6.0 to 8.0 wt. %, and more preferably 7.3 wt. %; and zincoxide (ZnO) in an amount of 3.0 to 5.0 wt. %, and preferably 4.8 wt. %,based on the total weight of the glass frits. The glass frits furtherinclude alkali metal oxides, such as oxides of lithium (Li), sodium(Na), and potassium (K), in a total amount of 2.0 to 6.0 wt. %, based onthe total weight of the glass frits. In the exemplary embodiment, theglass frits include the alkali metal oxides in a total amount of 4.7 wt.%, wherein 1.5 wt. % is lithium oxide and 3.1 wt. % is sodium oxide,based on the total weight of the glass frits. The glass frits alsoinclude alkaline earth metal oxides, such as oxides of magnesium (Mg),calcium (Ca), strontium (Sr), and barium (Ba) in a total amount of 3.0to 7.0 wt. %, based on the total weight of the glass frits. In theexemplary embodiment, the glass frits include the alkaline earth metaloxides in a total amount of 5.9 wt. %, wherein at least 2.95 wt. % isstrontium oxide and about 1.9 wt. % is magnesium oxide. However, it isnoted that other amounts of alkali metal oxides and alkaline earth metaloxides could be used. The glass frits and/or the powder used to form theglass seal 22 can also include small amounts of other components and/orimpurities.

Table 1 provides one exemplary powder composition used to form the glassseal 22 according to the present invention, in weight percent (wt. %),based on the total weight of the powder used to form the glass seal 22.

TABLE 1 Component Amount Glass Frits 77.85 Copper Flakes 20 SodiumBentonite 1 Lithium Carbonate 0.5 Polyethylene Glycol 0.15 Dextrin 0.5

Table 2 provides exemplary glass frit compositions according to thepresent invention, in weight percent (wt. %), based on the total weightof the glass frit composition.

TABLE 2 Overall Example Example Example Example Component Range Range 11 Range 2 2 Silicon Dioxide 22-40 35-40 38.6 22-28 25.1 Boron Oxide20-28 20-28 26.9 21-27 24.2 Alumina 10-22 10-15 11.7 16-22 18.4 BismuthOxide  5-15  5-10 7.3 10-15 12.5 Zinc Oxide  3-10 3-5 4.8  5-10 8.1Alkali Metal 2-6 2-6 4.7 2-5 2.8 Oxides Alkaline Earth  3-12 3-7 5.9 6-12 9.0 Metal Oxides

In the exemplary compositions of Table 2, the alkali metal oxidesinclude one or more of the group comprising lithium oxide, sodium oxideand potassium oxide. In one example, approximately one third of thealkali metal oxides is lithium oxide and approximately two thirds issodium oxide. However, any ratio of alkali metal oxides may be used. Thealkaline earth metal oxides of the exemplary composition include one ormore of the group comprising magnesium oxide, calcium oxide, strontiumoxide and barium oxide. In one example more than one half of thealkaline earth metal oxides is strontium oxide and approximately onethird is magnesium oxide. However, any ratio of alkaline earth metaloxides may be used. However, those of ordinary skill in the artunderstand that other types of alkali metals and alkaline earth metalscan be used in addition to, or in place of those listed.

The electrically conductive powder used to form the electricallyconductive glass seal 22 can be prepared using various differentmethods, including any method known in the art. Typically, the methodincludes obtaining the electrically conductive particles, binder,expansion agent, and glass fits, and mixing those components together.Once the components are mixed together, the electrically conductivematerial can be disposed in a bore of the insulator 26.

In one embodiment, prior to disposing the electrically conductivematerial in the insulator 26, the materials are mixed together by drymixing. Alternatively, the materials could be wet ground or mixed withwater to form a slurry, and then spray dried to form a plurality ofgranulated particles or powder. The spray drying step includes disposingthe slurry in a heated spray drier, wherein the slurry forms dropletswith water that flashes off in the heated spray dryer, leaving smallspherical granular particles. However, other methods can be used toprovide the electrically conductive material in particulate or powderform. For example the dry powders can be dry mixed in a mixer or blenderwith a small amount of water subsequently added which causes the powdermixture to agglomerate into granular particles, which may besubsequently dried or partially dried. The granules or powder arerelatively easy to handle, create little dust, and can be easily tampedor otherwise disposed in the bore of the insulator 26 around the centralelectrode 24, and around other electrically conductive components, ifdesired.

Once the electrically conductive material, typically the powder, isdisposed in the bore of the insulator 26, the insulator 26, centralelectrode 24 and electrically conductive material are fired together ina furnace, according to any method known in the art. During the firingstep, the components of the electrically conductive powder melt andexpand to fill at least a portion of the bore of the insulator 26 aroundthe central electrode 24, and thus form the electrically conductiveglass seal 22 providing the hermetic bond between the central electrode24 and the insulator 26. The firing temperature varies depending on thecomposition of the electrically conductive material, and in particularthe composition of the glass frits, but typically ranges from 600 to1000° C. For example, when the glass frits comprise the first examplecomposition of Table 2, the firing temperature ranges from 750 to 800°C., and when the glass frits comprise the second example composition ofTable 2, the firing temperature ranges from 650 to 700° C. In each case,the firing temperature is higher than the maximum temperature of theglass seal 22 during operation of the corona igniter 20.

Furthermore, at least a portion of the expansion agent converts from asolid to a gas and generates bubbles in the material during the firingstep, which causes the material to expand. The increase in volume of thematerial and the volume of the bore occupied by the electricallyconductive glass seal 22 can vary. The gas-filled bubbles lead togas-filled pores remaining in the electrically conductive glass seal 22after the firing step and when the glass seal 22 cools to roomtemperature. The gas-filled pores also remain in the glass seal 22 whenthe corona igniter 20 is used in the internal combustion engine.Typically, the fired glass seal 22 includes a plurality of gas-filledpores in an amount of 25.0 to 75.0 vol. %, and preferably 35.0 to 45.0vol. %, based on the total volume of the glass seal. The electricallyconductive particles prevent the potential for failure that could becaused by the gas-filled pores. Other than the change in mass of theexpansion agent and the burnt off binder, the composition does notsubstantially change during the firing step, and the fired glass seal 22has substantially the same composition as the starting powder.

FIGS. 2 and 2A illustrate the electrically conductive glass seal 22 ofFIG. 1, which includes the glass 21, electrically conductive metalparticles 23, and gas-filled pores 25 after the firing step. The pores25 have an approximately spherical shape and are spaced from one anotherby a matrix 27 comprising the metal particles 23 distributed in theglass 21. The metal particles 23 are distributed with sufficientelectrical contact between them such that the glass seal 22 iselectrically conductive. Although the pores 25 are close to one another,they are isolated from one another so that there is no transport of gasbetween them, and thus no transport of gas through the glass seal 22.

As shown in FIG. 1, the electrically conductive glass seal 22 typicallysurrounds a terminal end 28 of the central electrode 24 and alsosurrounds a portion of a terminal 30. However, although not shown, theglass seal 22 could also surround other electrically conductivecomponents disposed in the bore of the insulator 26, such as a resistoror a spring.

The corona igniter 20 including the electrically conductive glass seal22 of the present invention can have various different designs,including, but not limited to the design shown in FIG. 1. In theexemplary embodiment of FIG. 1, the central electrode 24 is disposed inthe bore of the insulator 26 beneath the terminal 30, and the terminal30 engages the terminal end 28 of the central electrode 24. The centralelectrode 24 is formed of an electrically conductive material, such asnickel or a nickel alloy. The central electrode 24 has a length Lextending along a center axis A from a terminal end 28 to a firing end32, wherein a majority of the length L of the central electrode 24 issurrounded by the insulator 26. The terminal end 28 of the centralelectrode 24 is supported and maintained in a predetermined axialposition by a reduced diameter of the insulator 26. Also in theexemplary embodiment, the central electrode 24 includes a firing tip 34at the firing end 32. The firing tip 34 has a plurality of branches eachextending radially outwardly from the center axis A for emitting anelectric field and providing the corona discharge during use of thecorona igniter 20 in the internal combustion engine.

The insulator 26 of FIG. 1 extends longitudinally along the center axisA from an insulator upper end 38 to an insulator nose end 40. Theinsulator 26 is formed of an insulating material, typically a ceramicsuch as such as alumina. The insulator 26 also presents an insulatorinner surface 42 surrounding the bore which extends longitudinally fromthe insulator upper end 38 to the insulator nose end 40 for receivingthe central electrode 24, terminal 30, and possibly other electricallyconductive components. The firing tip 34 of the central electrode 24 isdisposed longitudinally past the insulator nose end 40. The insulatorinner surface 42 presents an insulator inner diameter Di extendingacross and perpendicular to the center axis A. The insulator innerdiameter Di typically decreases along a portion of the insulator 26moving toward the insulator nose end 40 for supporting a portion of thecentral electrode 24 and maintaining the central electrode 24 in thepredetermined axial position.

The insulator 26 of the exemplary embodiment also presents an insulatorouter surface 44 having an insulator outer diameter Do extending acrossand perpendicular to the center axis A. The insulator outer surface 44extends longitudinally from the insulator upper end 38 to the insulatornose end 40. In the exemplary embodiment, the insulator outer diameterDo decreases along a portion of the insulator 26 adjacent the insulatornose end 40, moving toward the insulator nose end 40, to present aninsulator nose region 46. The insulator outer diameter Do also decreasesin a direction moving toward the insulator nose end 40 in a locationspaced from the insulator nose region 46, approximately at the middle ofthe insulator 26, to present an insulator lower shoulder 48. Theinsulator outer diameter Do also decreases along a portion of theinsulator 26 moving toward the insulator upper end 38 at a locationspaced from the insulator lower shoulder 48 to present an insulatorupper shoulder 50.

The corona igniter 20 also typically includes a shell 52 formed of metaland surrounding a portion of the insulator 26. The shell 52 is typicallyused to couple the insulator 26 to a cylinder block (not shown) of theinternal combustion engine. The shell 52 extends along the center axis Afrom a shell upper end 54 to a shell lower end 56. The shell upper end54 is disposed between the insulator upper shoulder 50 and the insulatorupper end 38 and engages the insulator 26. The shell lower end 56 isdisposed adjacent the insulator nose region 46 such that at least aportion of the insulator nose region 46 extends axially outwardly of theshell lower end 56.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings and may be practicedotherwise than as specifically described while within the scope of thefollowing claims.

What is claimed is:
 1. A corona igniter, comprising: an electricallyconductive component; an insulator surrounding said electricallyconductive component; an electrically conductive glass seal providing ahermetic bond between said electrically conductive component and saidinsulator; said electrically conductive glass seal including at leastone glass in a total amount of 50.0 to 85.0 wt. %, and electricallyconductive metal particles in an amount of 15.0 to 50.0 wt. %, based onthe total weight of said glass seal; wherein the glass seal includesgas-filled pores in an amount of 25.0 to 75.0 vol. %, based on the totalvolume of the glass seal; and said glass seal is electrical conductive.2. The corona igniter of claim 1, wherein said gas-filled pores arepresent in an amount of 35.0 to 45.0 vol. %, based on the total volumeof said glass seal and said gas-filled pores are spaced from one anotherby said glass and said electrically conductive metal particles.
 3. Thecorona igniter of claim 1, wherein said glass seal has an electricallyconductivity ranging from 9×10⁶ S/m to 65×10⁶ S/m.
 4. The corona igniterof claim 1, wherein said electrically conductive component includes acentral electrode surrounded by said insulator, and a firing tip at anend of said central electrode, said firing tip including a plurality ofbranches each extending radially outwardly from a center axis.
 5. Thecorona igniter of claim 1, wherein said at least one glass includessilica (SiO₂), boron oxide (B₂O₃), aluminum oxide (Al₂O₃), bismuth oxide(Bi₂O₃), and zinc oxide (ZnO); and said electrically conductiveparticles include copper.
 6. The corona igniter of claim 1, wherein saidat least one glass includes silica (SiO₂) in an amount of 35.0 to 40.0wt. %, boron oxide (B₂O₃) in an amount of 20.0 to 28.0 wt. %, aluminumoxide (Al₂O₃) in an amount of 10.0 to 15.0 wt. %, bismuth oxide (Bi₂O₃)in an amount of 10.0 to 15.0 wt. %, and zinc oxide (ZnO) in an amount of3.0 to 5.0 wt. %, based on the total weight of said at least one glass.7. The corona igniter of claim 6, wherein said at least one glassfurther include alkali metal oxides in a total amount of 2.0 to 6.0 wt.% and alkaline earth metal oxides in a total amount of 3.0 to 7.0 wt. %,based on the total weight of said at least one glass.
 8. The coronaigniter of claim 1, wherein said gas-filled pores are present in anamount of 35.0 to 45.0 vol. %, based on the total volume of said glassseal.
 9. The corona igniter of claim 1, wherein said gas-filled poresare spaced from one another by said glass and said electricallyconductive metal particles.
 10. The corona igniter of claim 1, whereinsaid electrically conductive metal particles include copper.
 11. Thecorona igniter of claim 10, wherein said electrically conductive metalparticles include flakes of the copper and have a particle size of lessthan 45 microns.
 12. The corona igniter of claim 1, wherein said glassseal has an electrical conductivity above 30×10⁶ S/m.